Biology research in radiation oncology has extensively utilized flow cytometric analyses over the years. We, at the Radiation Oncology Department of Washington University, are no exception. We have our first flow cytometer installed in 1978. We have since conducted numerous studies using flow cytometry, with minor improvements on the equipment applied during the ensuing years. With emerging emphasis in the application of molecular biology in radiation oncology research and vast advancement in fluorescent probe technology, however, the system currently available at this site has become outdated and insufficient to conduct desired experiments. The objective of this proposal is to request funds for the procurement of a flow cytometer/sorter to replace the currently available system at the Department of Radiation Oncology at Washington University School of Medicine. The system we are requesting funds for is FACSAria manufactured by BD Biosciences. The system as requested has all the features that are required to conduct research proposed by the current and future researchers in the Department as well as investigators from other departments who has been using our facility. Having three excitation wavelength and the capability to detect up to 9 fluorescence wavelengths allow us to conduct experiments in which relationship of several molecular and cellular parameters in each cell can be simultaneously assayed. Additionally the configuration of laser excitation and fluorescence detection for this system requires lower power for fluorochrome excitation, resulting in less damage to cells that are sorted and subsequently subcultured or assayed for molecular biology parameters that are sensitive to such insults. The Radiation Oncology biology laboratory is remotely located from the main campus of the Medical School. It is the only flow cytometry facility on the Medical School campus that has immediate access to ionizing radiation sources, a major component in our research. With the availability of wet laboratory and tissue culture facility also adjacent to the flow cytometry facility, this new flow cytometer offers flexibility in conducting experiments that cannot be obtained from other flow cytometry laboratories on the Medical School campus. [unreadable] [unreadable] [unreadable]